Re: [PATCH 3/3] arm64/cpufeature: Use helper macro to specify ID register for capabilites

[Will Deacon]

On Mon, Mar 06, 2023 at 10:20:25PM +0000, Mark Brown wrote:
> When defining which value to look for in a system register field we
> currently manually specify the register, field shift, width and sign and
> the value to look for. This opens the potential for error with for example
> the wrong field width or sign being specified, an enumeration value for
> a different similarly named field or letting something be initialised to 0.
> 
> Since we now generate defines for all the ID registers we now have named
> constants for all of these things generated from the system register
> description, meaning that we can generate initialisation for all the fields
> used in matching from a minimal specification of register, field and match
> value. This is both shorter and eliminates or makes build failures several
> potential errors.
> 
> No change in the generated binary.
> 
> Signed-off-by: Mark Brown <broonie@xxxxxxxxxx>
> ---
>  arch/arm64/kernel/cpufeature.c | 245 ++++++++---------------------------------
>  1 file changed, 44 insertions(+), 201 deletions(-)

[...]

>  		.desc = "WFx with timeout",
>  		.capability = ARM64_HAS_WFXT,
>  		.type = ARM64_CPUCAP_SYSTEM_FEATURE,
> -		.sys_reg = SYS_ID_AA64ISAR2_EL1,
> -		.sign = FTR_UNSIGNED,
> -		.field_pos = ID_AA64ISAR2_EL1_WFxT_SHIFT,
> -		.field_width = 4,
> -		.matches = has_cpuid_feature,
> -		.min_field_value = ID_AA64ISAR2_EL1_WFxT_IMP,
> +		ARM64_CPUID_FIELDS(ID_AA64ISAR2_EL1, WFxT, IMP)

You drop the '.matches' field here.

Will